Soil Testing, Soil Sampling, and Soil Fertility

Warren RobertsGeorge Kuepper

Self Diagnosis

• Plants• Soil

Nutrient Deficiencies

• Nitrogen (N)• Light Green Leaves, Older Leaves

• Phosphorus (P)

• Purple Leaves, Stunted Plants

• Potassium (K)• Yellow Margins on Older Leaves

Nutrient Deficiencies

• Micro Nutrients• Stripes

• Mottling

• Chlorosis

• Bleached

Excess N-P-K

• Nitrogen (N)• Dark Green Foliage, Poor Fruit Set

• Phosphorus (P)• Iron, Zinc Deficiencies

• Potassium (K)• Magnesium, Calcium Deficiencies

Soil Test

Fertility Management

• Nutrient Movement• Nitrogen• Phosphorus• Potassium

Fertility Management

• Soil Particles are Negatively Charged

Fertility Management

• Nitrogen• Exists as NO3 Anion

• (Negative Charge)• Does Not Bond with Soil Particles• Moves Rapidly in Water• Leaches Readily in Sandy Soils• Leaches More Slowly in Clay• Can be Lost in One Heavy Rain

• Sulfur Behaves Similarly to Nitrogen

Soil Fertility

N (lbs / acre)

0

10

20

30

40

50

60

70Before After

S (lbs / acre)

0

5

10

15

20

25

Desired Range

Before After

Fertility Management

• Phosphorus• Bonds with Soil Iron, Aluminum• Movement is Very Limited• Movement is Very Slow

• Takes Months or Years to Move

P Index

0

20

40

60

80

100

120

Desired Range

Before After

Fertility Management

• Potassium

• Has a Positive Charge

• Bonds to Negatively Charged Soil

• Moves Slightly Due to Water

K Index

0

50

100

150

200

250

Desired Range

Before After

Zn (ppm)

0

0.2

0.4

0.6

0.8

1

1.2

Desired Range

Before After

B (ppm)

0

0.05

0.1

0.15

0.2

0.25

0.3

Desired Range

Before After

Copper (ppm)

0

0.2

0.4

0.6

0.8

1

1.2

Desired Range

Before After

Soil Sampling• Results are Only as Good as the Sample

Soil Sampling• Random Variability

Number of Samples

• Depends on Soil

• Depends on Soil History

• Depends on Soil Treatments

• Usually 20 or more samples per field

Sampling Depth

• Root Zone

• Plow Layer

Eastern Oklahoma

• Acid pH in Soil

• Add Lime

Bentley, Oklahoma

Nitrogen Phosphorus Potassium ph Organic matter

3 45 174 5.5 1.14

2 27 147 5.4 0.76

2 13 176 5.2 1.01

3 20 130 5.5 0.98

4 17 171 5.7 1.48

9 15 417 4.8 1.34

Points to Remember

• Don’t Guess – Soil Test

• Sample thoroughly – 20 or more samples per field

• Sample root zone – normally 6 – 7 inches

Soil Aspects of Organic Farming

Warren Roberts